In article , says...

"George Pontis" wrote in message
...
There is a piece of dark bogwood in a community tank ...


Look he
http://www.aquarticles.com/articles/...i_Bogwood.html
In this article, it says of bogwood:

"b. If the bogwood is not petrified the living wood will rot underwater and
grow a white fungus. This does not harm the fish and can usually be brushed
off. "

Sounds like what you have?
-Jen

Great link Jen, a lot explained there. Some others have also identified it as most
likely a fungus. My thanks to all.

George